クラス UART -- 二重シリアル通信バス

UART は標準の UART/USART 二重シリアル通信プロトコルを実装しています。物理レベルでは RX と TX の２線で構成されています。通信の単位は 8 または 9 ビット幅の文字です(string 型の文字と混同しないでください)。

UART オブジェクトは以下をように作成、初期化できます:

from pyb import UART

uart = UART(1, 9600)                         # init with given baudrate
uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters

Bits can be 7, 8 or 9. Parity can be None, 0 (even) or 1 (odd). Stop can be 1 or 2.

Note: with parity=None, only 8 and 9 bits are supported. With parity enabled, only 7 and 8 bits are supported.

UART オブジェクトはストリーム(stream)オブジェクトのように機能し、読み書きは標準のストリームメソッドを使って行われます。

uart.read(10)       # 10文字を読み込んで、バイト列オブジェクトを返す
uart.read()         # 可能な限り文字を読み込む
uart.readline()     # 1行を読み込む
uart.readinto(buf)  # 読み込んで、与えたバッファに格納
uart.write('abc')   # 3文字を書き込む

Individual characters can be read/written using:

uart.readchar()     # read 1 character and returns it as an integer
uart.writechar(42)  # write 1 character

To check if there is anything to be read, use:

uart.any()          # returns the number of characters waiting

Note: The stream functions read, write, etc. are new in MicroPython v1.3.4. Earlier versions use uart.send and uart.recv.

コンストラクタ

class pyb.UART(bus, ...)

Construct a UART object on the given bus. For Pyboard bus can be 1-4, 6, 'XA', 'XB', 'YA', or 'YB'. For Pyboard Lite bus can be 1, 2, 6, 'XB', or 'YA'. For Pyboard D bus can be 1-4, 'XA', 'YA' or 'YB'. With no additional parameters, the UART object is created but not initialised (it has the settings from the last initialisation of the bus, if any). If extra arguments are given, the bus is initialised. See init for parameters of initialisation.

The physical pins of the UART busses on Pyboard are:

  • UART(4) is on XA: (TX, RX) = (X1, X2) = (PA0, PA1)
  • UART(1) is on XB: (TX, RX) = (X9, X10) = (PB6, PB7)
  • UART(6) is on YA: (TX, RX) = (Y1, Y2) = (PC6, PC7)
  • UART(3) is on YB: (TX, RX) = (Y9, Y10) = (PB10, PB11)
  • UART(2) is on: (TX, RX) = (X3, X4) = (PA2, PA3)

The Pyboard Lite supports UART(1), UART(2) and UART(6) only, pins are:

  • UART(1) is on XB: (TX, RX) = (X9, X10) = (PB6, PB7)
  • UART(6) is on YA: (TX, RX) = (Y1, Y2) = (PC6, PC7)
  • UART(2) is on: (TX, RX) = (X1, X2) = (PA2, PA3)

The Pyboard D supports UART(1), UART(2), UART(3) and UART(4) only, pins are:

  • UART(4) is on XA: (TX, RX) = (X1, X2) = (PA0, PA1)
  • UART(1) is on YA: (TX, RX) = (Y1, Y2) = (PA9, PA10)
  • UART(3) is on YB: (TX, RX) = (Y9, Y10) = (PB10, PB11)
  • UART(2) is on: (TX, RX) = (X3, X4) = (PA2, PA3)

Note: Pyboard D has UART(1) on YA, unlike Pyboard and Pyboard Lite that both have UART(1) on XB and UART(6) on YA.

メソッド

UART.init(baudrate, bits=8, parity=None, stop=1, *, timeout=0, flow=0, timeout_char=0, read_buf_len=64)

与えたパラメータで UART バスを初期化します。

  • baudrate is the clock rate.
  • bits is the number of bits per character, 7, 8 or 9.
  • parity is the parity, None, 0 (even) or 1 (odd).
  • stop is the number of stop bits, 1 or 2.
  • flow sets the flow control type. Can be 0, UART.RTS, UART.CTS or UART.RTS | UART.CTS.
  • timeout is the timeout in milliseconds to wait for writing/reading the first character.
  • timeout_char is the timeout in milliseconds to wait between characters while writing or reading.
  • read_buf_len is the character length of the read buffer (0 to disable).

This method will raise an exception if the baudrate could not be set within 5% of the desired value. The minimum baudrate is dictated by the frequency of the bus that the UART is on; UART(1) and UART(6) are APB2, the rest are on APB1. The default bus frequencies give a minimum baudrate of 1300 for UART(1) and UART(6) and 650 for the others. Use pyb.freq to reduce the bus frequencies to get lower baudrates.

Note: with parity=None, only 8 and 9 bits are supported. With parity enabled, only 7 and 8 bits are supported.

UART.deinit()

UART バスをオフにします。

UART.any()

Returns the number of bytes waiting (may be 0).

UART.read([nbytes])

Read characters. If nbytes is specified then read at most that many bytes. If nbytes are available in the buffer, returns immediately, otherwise returns when sufficient characters arrive or the timeout elapses.

If nbytes is not given then the method reads as much data as possible. It returns after the timeout has elapsed.

Note: for 9 bit characters each character takes two bytes, nbytes must be even, and the number of characters is nbytes/2.

戻り値: 読み込んだバイト列を含む bytes オブジェクト。タイムアウト時は None を返します。

UART.readchar()

Receive a single character on the bus.

Return value: The character read, as an integer. Returns -1 on timeout.

UART.readinto(buf[, nbytes])

buf にバイトを読み込みます。 nbytes が指定されている場合は、最大でそのバイト数を読み取ります。nbytes を指定しなかった場合は、最大で len(buf) バイト数を読み込みます。

戻り値: 読み込んで buf に格納したバイト数。タイムアウト時は None を返します。

UART.readline()

Read a line, ending in a newline character. If such a line exists, return is immediate. If the timeout elapses, all available data is returned regardless of whether a newline exists.

Return value: the line read or None on timeout if no data is available.

UART.write(buf)

Write the buffer of bytes to the bus. If characters are 7 or 8 bits wide then each byte is one character. If characters are 9 bits wide then two bytes are used for each character (little endian), and buf must contain an even number of bytes.

Return value: number of bytes written. If a timeout occurs and no bytes were written returns None.

UART.writechar(char)

Write a single character on the bus. char is an integer to write. Return value: None. See note below if CTS flow control is used.

UART.sendbreak()

Send a break condition on the bus. This drives the bus low for a duration of 13 bits. Return value: None.

定数

UART.RTS
UART.CTS

to select the flow control type.

Flow Control

On Pyboards V1 and V1.1 UART(2) and UART(3) support RTS/CTS hardware flow control using the following pins:

  • UART(2) is on: (TX, RX, nRTS, nCTS) = (X3, X4, X2, X1) = (PA2, PA3, PA1, PA0)
  • UART(3) is on :(TX, RX, nRTS, nCTS) = (Y9, Y10, Y7, Y6) = (PB10, PB11, PB14, PB13)

On the Pyboard Lite only UART(2) supports flow control on these pins:

(TX, RX, nRTS, nCTS) = (X1, X2, X4, X3) = (PA2, PA3, PA1, PA0)

In the following paragraphs the term "target" refers to the device connected to the UART.

When the UART's init() method is called with flow set to one or both of UART.RTS and UART.CTS the relevant flow control pins are configured. nRTS is an active low output, nCTS is an active low input with pullup enabled. To achieve flow control the Pyboard's nCTS signal should be connected to the target's nRTS and the Pyboard's nRTS to the target's nCTS.

CTS: target controls Pyboard transmitter

If CTS flow control is enabled the write behaviour is as follows:

If the Pyboard's UART.write(buf) method is called, transmission will stall for any periods when nCTS is False. This will result in a timeout if the entire buffer was not transmitted in the timeout period. The method returns the number of bytes written, enabling the user to write the remainder of the data if required. In the event of a timeout, a character will remain in the UART pending nCTS. The number of bytes composing this character will be included in the return value.

If UART.writechar() is called when nCTS is False the method will time out unless the target asserts nCTS in time. If it times out OSError 116 will be raised. The character will be transmitted as soon as the target asserts nCTS.

RTS: Pyboard controls target's transmitter

If RTS flow control is enabled, behaviour is as follows:

If buffered input is used (read_buf_len > 0), incoming characters are buffered. If the buffer becomes full, the next character to arrive will cause nRTS to go False: the target should cease transmission. nRTS will go True when characters are read from the buffer.

Note that the any() method returns the number of bytes in the buffer. Assume a buffer length of N bytes. If the buffer becomes full, and another character arrives, nRTS will be set False, and any() will return the count N. When characters are read the additional character will be placed in the buffer and will be included in the result of a subsequent any() call.

If buffered input is not used (read_buf_len == 0) the arrival of a character will cause nRTS to go False until the character is read.